Possibility of increasing the brightness of lasers passively $Q$-switched with the aid of LiF crystals containing $F_2^-$ color centers

A YAG:Nd$^{3+}$ laser was passively $Q$-switched with the aid of an LiF crystal which contained $F_2^-$ color centers and was characterized by an initial transmission that varied across the crystal. Such switching reduced the angular divergence of the neodymium laser radiation to 2' without altering the energy characteristics. A method was developed for determining the initial transmission profile of a passive $Q$ switch. An increase in the efficiency of the recovery of the $F_2^+$ color centers in an LiF crystal containing $F_2$ centers was observed under the simultaneous action of the second and third harmonics of the neodymium laser radiation.